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Aims: Trans/transfeminine women are disproportionally affected by HIV. Concerns regarding negative drug-drug interactions (DDIs) between ART drugs and gender-affirming hormone therapy (GAHT), specifically feminizing hormone therapy (FHT), may contribute to the lower ART uptake by trans women with HIV compared with their cis counterparts. The aim of this study is to investigate the bidirectional pharmacokinetic effects of components of FHT regimens (oral oestradiol and androgen-suppressing medications) with the ART regimen (bictegravir/emtricitabine/tenofovir alafenamide [B/F/TAF)]., Methods: We present a protocol for a three-armed, parallel-group, longitudinal (6-month), DDI study. Group 1 includes 15 3trans women with HIV taking FHT and ART; group 2 includes 15 premenopausal cis women with HIV taking ART; group 3 includes 15 trans women without HIV taking FHT. Women with HIV must be on or switch to B/F/TAF at baseline and be virally suppressed for ≥3 months. Trans women must be taking a stable regimen of ≥2 mg daily oral oestradiol and an anti-androgen (pharmaceutical, and/or surgical, and/or medical) for ≥3 months. Plasma ART drug concentrations will be sampled at Month 2 and compared between groups 1 and 2. Serum oestradiol concentrations will be sampled at baseline and Month 2 visits and compared between groups 1 and 3. The primary outcomes are B/F/TAF pharmacokinetic parameters (C min , C max and AUC) and oestradiol concentrations (C min , C 4h, C max and AUC) at month 2., Discussion: This study is of global importance as it provides critical information regarding safe coadministration of B/F/TAF and FHT, both of which are life-saving therapies for trans women with HIV., (© 2024 The Author(s). British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Background Feminizing hormone therapy (FHT) is essential to many trans women. Concern about negative drug interactions between FHT and ART can be an ART adherence barrier among trans women with HIV. Objectives In this single-centre, parallel group, cross-sectional pilot study, we measured serum oestradiol concentrations in trans women with HIV taking FHT and unboosted integrase strand transfer inhibitor (INSTI)-based ART versus trans women without HIV taking FHT. Methods We included trans women with and without HIV, aged ≥18 years, taking ≥2 mg/day of oral oestradiol for at least 3 months plus an anti-androgen. Trans women with HIV were on suppressive ART ≥3 months. Serum oestradiol concentrations were measured prior to medication dosing and 2, 4, 6 and 8 h post-dose. Median oestradiol concentrations were compared between groups using Wilcoxon rank-sum tests. Results Participants (n  = 8 with HIV, n  = 7 without) had a median age of 32 (IQR: 28, 39) years. Among participants, the median oral oestradiol dose was 4 mg (range 2–6 mg). Participants had been taking FHT for a median of 4 years (IQR: 2, 8). Six trans women with HIV were taking bictegravir/emtricitabine/tenofovir alafenamide and two were taking dolutegravir/abacavir/lamivudine. All oestradiol concentrations were not significantly different between groups. Eleven (73%) participants had target oestradiol concentrations in the range 200–735 pmol/L at C 4h (75% among women with HIV, 71% among those without HIV). Conclusions Oestradiol concentrations were not statistically different in trans women with HIV compared with those without HIV, suggesting a low probability of clinically relevant drug–drug interactions between FHT and unboosted INSTI-based ART. [ABSTRACT FROM AUTHOR]